$A_{\mathrm{c}}$	Cross-section area: ${\mathrm{m}}^2$
$C_{\mathrm{p}}$	Molar heat capacity, $\mathrm{J}\cdot {\mathrm{mol}}^{-1}\cdot {\mathrm{K}}^{-1}$
$c$	Dimensionless coefficient of variation
$d$	Diameter, $\mathrm{m}$
$G$	Mass flow rate per unit area, ${\mathrm{kg} \mathrm{s}}^{-1}{\mathrm{m}}^{-2}$
$F$	Molar flow rate, $\mathrm{mol}\cdot {\mathrm{s}}^{-1}$
$H$	Hamiltonian function of the optimal problem
$K_{{\mathrm{I}}_2}$	Adsorption equilibrium constant of iodine, ${\mathrm{bar}}^{-1}$
$K_{\mathrm{p}}$	Equilibrium constant
$k$	Reaction rate constant, ${\mathrm{mol} \mathrm{s}}^{-1}{\mathrm{kg}}^{-1}$
$L$	Length, $m$
$M$	Molar mass, ${\mathrm{kg} \mathrm{mol}}^{-1}$
$P$	Total pressure, $\mathrm{bar}$
$p$	Partial pressure of reaction component gas, $\mathrm{bar}$
$q$	Heat flow per unit area, ${\mathrm{W} \mathrm{m}}^{-2}$
$U$	Overall heat transfer coefficient, $\mathrm{W} {\mathrm{m}}^{-2}{ \mathrm{K}}^{-1}$
$u$	Control variable
$v$	Superficial velocity, ${\mathrm{m} \mathrm{s}}^{-1}$
$R$	Universal gas constant, ${\mathrm{J} \mathrm{mol} \mathrm{K}}^{-1}$
$Re$	Reynolds number
$r$	Chemical reaction rate, ${\mathrm{mol} \mathrm{s}}^{-1}{ \mathrm{kg}}^{-1}$
$S$	Entropy, ${\mathrm{J} \mathrm{K}}^{-1}{ \mathrm{mol}}^{-1}$
$\left(\mathrm{d}S/\mathrm{d}t\right)$	Entropy generation rate, ${\mathrm{J} \mathrm{K}}^{-1}{ \mathrm{s}}^{-1}$
$T$	Temperature, $\mathrm{K}$
$x$	Gas mole fraction
$x$	State variable vector
$z$	Axial coordinate